#28727: sqlite: CAST to DATE causes error
-------------------------------------+-------------------------------------
     Reporter:  direx                |                    Owner:  nobody
         Type:  Bug                  |                   Status:  new
    Component:  Database layer       |                  Version:  1.11
  (models, ORM)                      |
     Severity:  Normal               |               Resolution:
     Keywords:                       |             Triage Stage:
                                     |  Unreviewed
    Has patch:  0                    |      Needs documentation:  0
  Needs tests:  0                    |  Patch needs improvement:  0
Easy pickings:  0                    |                    UI/UX:  0
-------------------------------------+-------------------------------------

Old description:

> When trying to cast a date object to a `DateField` in `annotate` an
> exception is raised:
>
> {{{
> import datetime
> from django.contrib.auth.models import User
> from django.db import models
> from django.db.models.functions import Cast
>
> User.objects.all().annotate(today=Cast(datetime.date.today(),
> models.DateField()))
>
> ...
>
> TypeError: expected string or buffer
> }}}
>
> This only seems to happen with SQLite, MySQL works as expected.
>
> FYI, this is the SQL which is generated for SQLite:
>
> {{{
> SELECT "auth_user"."id", "auth_user"."password",
> "auth_user"."last_login", "auth_user"."is_superuser",
> "auth_user"."username", "auth_user"."first_name",
> "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff",
> "auth_user"."is_active", "auth_user"."date_joined", CAST(2017-10-20 AS
> date) AS "today" FROM "auth_user"
> }}}

New description:

 When trying to cast a date object to a `DateField` in `annotate` an
 exception is raised:

 {{{
 import datetime
 from django.contrib.auth.models import User
 from django.db import models
 from django.db.models.functions import Cast

 User.objects.get_or_create(username="test")
 User.objects.all().annotate(today=Cast(datetime.date.today(),
 models.DateField()))

 Traceback (most recent call last):
   File "<console>", line 1, in <module>
   File "/tmp/testenv/lib/python2.7/site-
 packages/django/db/models/query.py", line 226, in __repr__
     data = list(self[:REPR_OUTPUT_SIZE + 1])
   File "/tmp/testenv/lib/python2.7/site-
 packages/django/db/models/query.py", line 250, in __iter__
     self._fetch_all()
   File "/tmp/testenv/lib/python2.7/site-
 packages/django/db/models/query.py", line 1118, in _fetch_all
     self._result_cache = list(self._iterable_class(self))
   File "/tmp/testenv/lib/python2.7/site-
 packages/django/db/models/query.py", line 62, in __iter__
     for row in compiler.results_iter(results):
   File "/tmp/testenv/lib/python2.7/site-
 packages/django/db/models/sql/compiler.py", line 842, in results_iter
     row = self.apply_converters(row, converters)
   File "/tmp/testenv/lib/python2.7/site-
 packages/django/db/models/sql/compiler.py", line 827, in apply_converters
     value = converter(value, expression, self.connection,
 self.query.context)
   File "/tmp/testenv/lib/python2.7/site-
 packages/django/db/backends/sqlite3/operations.py", line 227, in
 convert_datefield_value
     value = parse_date(value)
   File "/tmp/testenv/lib/python2.7/site-
 packages/django/utils/dateparse.py", line 61, in parse_date
     match = date_re.match(value)
 TypeError: expected string or buffer

 }}}

 This only seems to happen with SQLite, MySQL works as expected.

 FYI, this is the SQL which is generated for SQLite:

 {{{
 SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login",
 "auth_user"."is_superuser", "auth_user"."username",
 "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email",
 "auth_user"."is_staff", "auth_user"."is_active",
 "auth_user"."date_joined", CAST(2017-10-20 AS date) AS "today" FROM
 "auth_user"
 }}}

--

Comment (by direx):

 OK, I have updated the original text in the ticket to include the full
 stracktrace.

 Replying to [comment:1 Simon Charette]:
 > Also, I think you'd want to use
 `annotate(today=Value(datetime.date.today()))` instead.
 Actually I am doing something entirely different (I need `Coalesce()` and
 `Max()`) and ran into this issue right there. The above code is just a
 minimum demonstration on how the bug can be triggered. I know that the
 code doesn't actually make sense, but I did not want to make the generated
 query more complex than it has to be for the example.

-- 
Ticket URL: <https://code.djangoproject.com/ticket/28727#comment:2>
Django <https://code.djangoproject.com/>
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